/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
        if(headA==nullptr || headB==nullptr)
            return nullptr;
        ListNode* pa = headA;
        ListNode* pb = headB;
        while(pa != pb){
            pa = pa==nullptr? headB:pa->next;
            pb = pb==nullptr? headA:pb->next;
        }
        return pa;
    }
};